1. Field of the Invention
The present invention relates to lithographic projection apparatus, and more particularly to apparatus including conduits for providing utilities such as power, water, control signals and gases through cables, hoses or pipes to a movable component in a vacuum chamber.
2. Background of the Related Art
A lithographic projection apparatus in accordance with the present invention generally includes a radiation system for providing a projection beam of radiation, a first object table for supporting patterning structure, the patterning structure serving to pattern the projection beam according to a desired pattern, a second object table for holding a substrate, a vacuum chamber provided with a first gas evacuating means for generating a vacuum beam path for the projection beam, a projection system for projecting the patterned beam onto a target portion of the substrate and conduits for providing utilities to a component moveable in at least one degree of freedom in said vacuum chamber.
The term xe2x80x9cpatterning structurexe2x80x9d as here employed should be broadly interpreted as referring to means that can be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate; the term xe2x80x9clight valvexe2x80x9d can also be used in this context. Generally, the said pattern will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit or other device (see below). Examples of such patterning structure include:
A mask. The concept of a mask is well known in lithography, and it includes mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. Placement of such a mask in the radiation beam causes selective transmission (in the case of a transmissive mask) or reflection (in the case of a reflective mask) of the radiation impinging on the mask, according to the pattern on the mask. In the case of a mask, the first object table will generally be a mask table, which ensures that the mask can be held at a desired position in the incoming radiation beam, and that it can be moved relative to the beam if so desired.
A programmable mirror array. An example of such a device is a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such an apparatus is that (for example) addressed areas of the reflective surface reflect incident light as diffracted light, whereas unaddressed areas reflect incident light as undiffracted light. Using an appropriate filter, the said undiffracted light can be filtered out of the reflected beam, leaving only the diffracted light behind; in this manner, the beam becomes patterned according to the addressing pattern of the matrix-addressable surface. The required matrix addressing can be performed using suitable electronic means. More information on such mirror arrays can be gleaned, for example, from U.S. Pat. Nos. 5,296,891 and 5,523,193, which are incorporated herein by reference. In the case of a programmable mirror array, the first object table may be embodied as a frame or table, for example, which may be fixed or movable as required.
A programmable LCD array. An example of such a construction is given in U.S. Pat. No. 5,229,872, which is incorporated herein by reference. As above, the first object table in this case may be embodied as a frame or table, for example, which may be fixed or movable as required.
For purposes of simplicity, the rest of this text may, at certain locations, specifically direct itself to examples involving a mask and mask table; however, the general principles discussed in such instances should be seen in the broader context of the patterning structure as hereabove set forth.
Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, the patterning structure may generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising one or more dies) on a substrate (silicon wafer) that has been coated with a layer of radiation-sensitive material (resist). In general, a single wafer will contain a whole network of adjacent target portions that are successively irradiated via the projection system, one at a time. In current apparatus, employing patterning by a mask on a mask table, a distinction can be made between two different types of machine. In one type of lithographic projection apparatus, each target portion is irradiated by exposing the entire mask pattern onto the target portion at once; such an apparatus is commonly referred to as a wafer stepper. In an alternative apparatusxe2x80x94commonly referred to as a step-and-scan apparatusxe2x80x94each target portion is irradiated by progressively scanning the mask pattern under the projection beam in a given reference direction (the xe2x80x9cscanningxe2x80x9d direction) while synchronously scanning the substrate table parallel or anti-parallel to this direction; since, in general, the projection system will have a magnification factor M (generally  less than 1), the speed V at which the substrate table is scanned will be a factor M times that at which the mask table is scanned. More information with regard to lithographic devices as here described can be gleaned, for example, from U.S. Pat. No. 6,046,792, incorporated herein by reference.
In a manufacturing process using a lithographic projection apparatus, a pattern (e.g. in a mask) is imaged onto a substrate that is at least partially covered by a layer of radiation-sensitive material (resist). Prior to this imaging step, the substrate may undergo various procedures, such as priming, resist coating and a soft bake. After exposure, the substrate may be subjected to other procedures, such as a post-exposure bake (PEB), development, a hard bake and measurement/inspection of the imaged features. This array of procedures is used as a basis to pattern an individual layer of a device, e.g. an IC. Such a patterned layer may then undergo various processes such as etching, ion-implantation (doping), metallization, oxidation, chemo-mechanical polishing, etc., all intended to finish off an individual layer. If several layers are required, then the whole procedure, or a variant thereof, will have to be repeated for each new layer. Eventually, an array of devices will be present on the substrate (wafer). These devices are then separated from one another by a technique such as dicing or sawing, whence the individual devices can be mounted on a carrier, connected to pins, etc. Further information regarding such processes can be obtained, for example, from the book xe2x80x9cMicrochip Fabrication: A Practical Guide to Semiconductor Processingxe2x80x9d, Third Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN 0-07-067250-4, incorporated herein by reference.
For the sake of simplicity, the projection system may hereinafter be referred to as the xe2x80x9clensxe2x80x9d; however, this term should be broadly interpreted as encompassing various types of projection system, including refractive optics, reflective optics, and catadioptric systems, for example. The radiation system may also include components operating according to any of these design types for directing, shaping or controlling the projection beam of radiation, and such components may also be referred to below, collectively or singularly, as a xe2x80x9clensxe2x80x9d. Further, the lithographic apparatus may be of a type having two or more substrate tables (and/or two or more mask tables). In such xe2x80x9cmultiple stagexe2x80x9d devices the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposures. Twin stage lithographic apparatus are described, for example, in U.S. Pat. No. 5,969,441 and WO 98/40791, incorporated herein by reference.
In a lithographic apparatus, the size of features that can be imaged onto the substrate is limited by the wavelength of the projection radiation. To produce integrated circuits with a higher density of devices and hence higher operating speeds, it is desirable to be able to image smaller features. While most current lithographic projection apparatus employ ultraviolet light generated by mercury lamps or excimer lasers, it has been proposed to use shorter wavelength radiation of around 13 nm. Such radiation is termed extreme ultraviolet (EUV) or soft x-ray, and possible sources include laser produced plasma sources, discharge plasma sources or synchrotron radiation from electron storage rings. An outline design of a lithographic projection apparatus using synchrotron radiation is described in xe2x80x9cSynchrotron radiation sources and condensers for projection x-ray lithographyxe2x80x9d, J B Murphy et al, Applied Optics Vol. 32 No. 24 pp 6920-6929 (1993).
Other proposed radiation types include electron beams and ion beams. Further information with regard to the use of electron beams in lithography can be gleaned, for example, from U.S. Pat. Nos. 5,079,122 and 5,260,151, as well as from EP-A-0 965 888. These types of beam share with EUV the requirement that the beam path, including the mask, substrate and optical components, be kept in a high vacuum. This is to prevent absorption and/or scattering of the beam, whereby a total pressure of less than about 10xe2x88x926 millibar is typically necessary for such charged particle beams. Otherwise, for apparatus using EUV radiation, the total vacuum pressure need only be between 10xe2x88x923 and 10xe2x88x925 millibar. Optical elements for EUV radiation can be spoiled, by the deposition of carbon layers on their surface, which imposes the additional requirement that hydrocarbon partial pressures should generally be kept as low as possible, for example below 10xe2x88x928 or 10xe2x88x929 millibar.
Working in a high vacuum imposes quite onerous conditions on the components that must be put into the vacuum. For components inside the vacuum chamber, materials that minimize or eliminate contaminant and total outgassing, i.e. both outgassing from the materials themselves and from gases adsorbed on their surfaces, should be used. It has been found that for the desired degree of movement required by the object holders, conduits can be made of plastics materials such that they are flexible enough. These types of materials often are deleterious to the vacuum in the vacuum chamber because outgassing of contaminants as described above will occur. There are plastics better suited for vacuum applications (for example teflon) but the large number of cables and lines which are required to be lead through the vacuum present a large surface area to outgassing of contaminants. It will be difficult to get a partially hydrocarbon pressure below 10xe2x88x928 or 10xe2x88x929 millibar, for example, when plastic conduits are used. Furthermore, the risk of leaks from conduits makes their use impractical. It would be very desirable to be able to reduce the use of conduits. However, conventional designs of substrate, mask and transfer stages are very complicated and employ large numbers of sensors and drive arrangements, which all need a large numbers of conduits for conveying water and gases and for protecting electric wiring.
To circumvent this problem it has been proposed in U.S. Pat. No. 4,993,696 to use metal pipes made of stainless material for the supply and exhaustion of an operating fluid or gas in a vacuum ambience. Two adjacent pipes may then be coupled with each other by a joint, which is arranged to allow swingable movement of one of the pipes relative to the other. The metal pipes will not suffer from outgassing as the nylon conduits will do. A disadvantage of the joints is that it is very difficult to design joints that are totally closed for fluids or gases in a vacuum environment. Therefor there may be leakage of gases through the joint to the vacuum environment that will contaminate the vacuum environment.
Another solution has been proposed by European Patent Application 1052549. In this publication conduits are fed through hollow pipes that are rigidly connected to a movable object table and which pipes are used to transfer movements from outside a vacuum chamber to said table. The pipes are hollow and the pressure within the pipes is equal to the pressure outside the vacuum chamber. Between the wall of the vacuum chamber and the pipes differentially pumped seals are used to prevent the leakage of air to the vacuum chamber and at the same time allowing for movement of the object table.
One aspect of the present invention provides a lithographic apparatus with substantially reduced problems due to out-gassing of materials in the vacuum chamber.
According to the present invention there is provided a lithographic projection apparatus comprising:
a radiation system for providing a projection beam of radiation;
a first object table for supporting patterning structure, the patterning structure serving to pattern the projection beam according to a desired pattern;
a second object table for holding a substrate;
a vacuum chamber provided with a first gas evacuating means for generating a vacuum beam path for the projection beam;
a projection system for projecting the patterned beam onto a target portion of the substrate; and
conduits for providing utilities to a component moveable in at least one degree of freedom in said vacuum chamber, characterized in that the apparatus further comprises:
a conduit shield for shielding the vacuum of said vacuum chamber from a space comprising the conduits, said conduct shield being constructed and arranged to allow for movement of the component in said at least one degree of freedom, and
a second gas evacuating means for providing a vacuum in the space comprising the conduits.
The term utilities as here employed refers to the water, gas, electricity and signals that must be provided to the moveable component. The term conduit refers to the cables and tubes that are used to transport the utilities to the moveable component. More specifically the term conduits refers to such items as power cords, signal carriers, gas tubes (e.g. for supplying gas to a gas bearing in the table), coolant tubes, etc. Moveable components inside the vacuum chamber including the mask table and/or the substrate table and/or associated motors and/or sensors may be connected to a frame outside the vacuum chamber in this manner (using a distinct conduit conduct for each component).
It will be difficult to make the conduit shield airtight and at the same time flexible enough to allow for movement of the component. The inventors have solved this problem by the use of a conduit shield that will shield the vacuum chamber from the space comprising the conduits but need not to be completely airtight. The leakage through the not completely airtight conduit shield will be minimized by having a small or even no pressure difference between the vacuum in the vacuum chamber and the space comprising the conduits. The conduits will be in a space that is made vacuum by a second gas evacuating means and that will become dirty due to outgassing of the conduits. The dirty vacuum in the space comprising the conduits will not negatively effect the vacuum in the vacuum chamber because the use of the almost airtight conduit shield and the little pressure difference that exists between the space comprising the conduits and the vacuum chamber. The outflow of contaminants through the not completely airtight conduit shield to the vacuum chamber will thereby be minimized. At the same time the loosened requirements for the airtightness of the conduit shield will make it more easy to construct a conduit shield that allows for movement of the movable component. An other advantage of the construction according to the invention is that the force exerted on the conduit shield by any gas pressure in the space comprising the conduits is decreased by the second gas evacuating means so that lighter building materials can be used.
The vacuum in the vacuum chamber may have a hydrocarbon partial pressures below 10xe2x88x928 or 10xe2x88x929 millibar, for example, while that partial pressure in the space comprising the conduits will be substantial higher. The vacuum provided to the space comprising the conduits may be around 10xe2x88x923 millibar and the vacuum provided to the vacuum chamber may be around 10xe2x88x925 millibar or lower in the presence of the optical components.
According to a second aspect of the present invention there is provided a device manufacturing method comprising the steps of:
providing a substrate that is at least partially covered by a layer of radiation-sensitive material;
providing a vacuum to a first vacuum chamber;
providing utilities through conduits to at least one component moveable in at least a first direction in said first vacuum chamber;
projecting a projection beam of radiation using a radiation system through said vacuum chamber;
using patterning structure to endow the projection beam with a pattern in its cross-section;
projecting the patterned projection beam of radiation onto a target portion of the layer of radiation-sensitive material,
characterized in that the method comprises the steps of:
shielding said vacuum in said vacuum chamber with a conduit shield from said conduits,
moving said conduit shield so as to follow the moveable component; and
providing a second vacuum in a space comprising the conduits and separated by the conduit shield from said vacuum chamber.
Although specific reference may be made in this text to the use of the apparatus according to the invention in the manufacture of ICs, it should be explicitly understood that such an apparatus has many other possible applications. For example, it may be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid-crystal display panels, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms xe2x80x9creticlexe2x80x9d, xe2x80x9cwaferxe2x80x9d or xe2x80x9cdiexe2x80x9d in this text should be considered as being replaced by the more general terms xe2x80x9cmaskxe2x80x9d, xe2x80x9csubstratexe2x80x9d and xe2x80x9ctarget portionxe2x80x9d, respectively.